1. Field of the Invention
The present invention relates to a three-dimensional image display device and a three-dimensional image display method.
2. Related Art
There are various known systems for stereoscopic image display devices or so-called three-dimensional display devices that can display moving images. In recent years, there is an increasing demand for flat-panel type devices that do not require any special tools such as glasses. One of the systems that can be easily realized is a system in which an optical plate for directing the light rays from a display panel (an elemental image display unit) toward a viewer is placed in front of the display panel of a device such as a liquid crystal display device or a plasma display device of a direct-vision type or a projection type having the pixel positions fixed therein.
An optical plate is generally called a parallax barrier, and controls light rays so that different images can be seen from the same position on the optical plate at different angles. More specifically, in a case where only transverse parallaxes (horizontal parallaxes) are provided, slits or a lenticular sheet (a cylindrical lens array) is employed. In a case where vertical parallaxes are also provided, a pinhole array or a lens array is employed. The systems utilizing parallax barriers include the binocular system, the multi-viewpoint system, the super multi-viewpoint system (the multi-viewpoint system involving a very large number of viewpoints), and the integral photography (hereinafter referred to as IP). The basic principles of those systems are substantially the same as those developed a hundred years ago and used for stereoscopic photography.
In the IP system or the multi-viewpoint system, the viewing distance is normally limited, and therefore, an image to be displayed is formed so that the perspective projection image at the viewing distance can be actually seen. In the IP system provided only with horizontal parallaxes (the one-dimensional IP system), there are combinations of parallel light rays where the horizontal pitch of the parallax barrier is equivalent to an integral multiple of the value of the horizontal pitch of sub-pixels of the elemental image display unit (this system will be hereinafter referred to also as the parallel-ray one-dimensional IP). Therefore, images that are perspective projection images at a constant viewing distance in the vertical direction and are orthographic projection images in the horizontal direction are divided into the images of the respective pixel columns, and the divided images are combined to form a parallax interleaved image in the image format to be displayed in the display plane. In this manner, a correctly projected three-dimensional image can be obtained. The specific procedures are disclosed in SID04 Digest 1438 (2004). In the multi-viewpoint system, an image formed through a simple perspective projection is divided and rearranged, so as to obtain a correctly projected three-dimensional image.
An image pick-up device that utilizes different projecting methods and different projection center distances between the vertical direction and the horizontal direction is difficult to produce, because cameras or lenses of the same size as the object to be displayed are required, especially in a orthographic projecting operation. Therefore, to achieve orthographic projection data through an image pick-up operation, conversion of the image pick-up data of a perspective projection image is more realistic. For example, a light-ray space method or the like by which interpolations utilizing an EPI (epipolar plane) are performed is well known.
As disclosed in SID04 Digest 1438 (2004), the parallel-ray one-dimensional IP system has a wider viewing zone and more continuous motion parallaxes than the binocular system and the multi-viewpoint system. Accordingly, in the parallel-ray one-dimensional IP system, images can be easily viewed, without a feeling of discomfort.
Since the binocular system and the multi-viewpoint system are the simplest three-dimensional image display systems, the image formats are also simple, and all viewpoint images have the same sizes. Two parallax components images in a binocular case and nine parallax components images in a nine-viewpoint case are divided into images of the respective pixel columns, and the divided images are combined to form a parallax interleaved image (elemental image array) in the image format to be displayed on the elemental image display unit. In the parallel-ray one-dimensional IP system, the number of parallax component images is larger than that in a multi-viewpoint system having the same resolution, and the sizes (the horizontal use ranges) of the parallax components images vary with the parallax directions. However, JP-A 2006-98779 (KOKAI) discloses that, in the parallel-ray one-dimensional IP system, tiling can be efficiently performed on the parallax component images in suitable combinations only in the necessary ranges, and the parallax components images can be converted, with high efficiency, into a format that causes little degradation at the time of non-reversed compression.
In any of one-dimensional IP systems, two-dimensional IP systems, and multi-viewpoint systems involving many parallaxes, when a viewer is located on a viewing zone boundary, a pseudoscopic image or an abnormal (broken) image having several vertical lines running therein is observed. To prevent this, JP-A 2004-258210 (KOKAI) discloses a method by which alarm image data is arranged on the boundaries between elemental images, so that an alarm image, instead of a broken image, can be observed.
However, in a case where crosstalk between parallax components is utilized to provide continuous motion parallaxes, an alarm image placed on the boundary between elemental images might be recognized as a periodic pattern with only small gradations and is hardly visible. If the area of the alarm image is increased so as to be more easily recognized, the viewing zone for three-dimensional displays is narrowed. Also, since the process of inserting an alarm image to an image is not simple, the processing load is increased.
As described above, in a three-dimensional image display device of the conventional parallel-ray one-dimensional IP type, an alarm image placed on the boundary between elemental images is not easily recognized, and it is difficult to use an alarm image without a reduction of the viewing zone or a decrease in processing speed.